The present invention relates to a fuel cell unit which comprises a cathode-anode-electrolyte unit and a contact plate which is in electrically conductive contact with the cathode-anode-electrolyte unit (CAE unit).
Fuel cell units of this type are known from the state of the art.
As a rule, several such fuel cell units are combined to form a composite block of fuel cells, in which the fuel cell units follow one another along a stacking direction.
In the cathode-anode-electrolyte unit, an electrochemical reaction takes place during the operation of the fuel cell unit, during the course of which electrons are supplied to the anode of the CAE unit and electrons withdrawn from the cathode of the CAE unit for the ionization of oxygen atoms. The contact plates arranged between the CAE units of two consecutive fuel cell units serve to balance the charge between the cathode of the one fuel cell unit and the anode of the adjacent fuel cell unit in order to supply the cathode with the electrons required for the ionization. Electric charges may be tapped from the edge-side contact plates of the composite block of fuel cells in order to supply them to an external useful current circuit.
The contact plates used with the known fuel cell units are metal plates which are milled or eroded from the entire plate and between which the CAE units are inserted so that these contact plates serve at the same time to hold the CAE units, as well. Furthermore, these plates are provided with channels which serve for the passage of fluids (combustible gas, oxidation agent and/or refrigerant) through the fuel cell unit.
These known fuel cell units are very complicated to produce and thus suitable only for small quantities.
The object underlying the present invention is therefore to create a fuel cell unit of the type specified at the outset which requires only small production resources and is thus suitable for large-scale production.
This object is accomplished in accordance with the invention, in a fuel cell unit with the features of the preamble to claim 1, in that the fuel cell unit comprises a fluid guiding element which is connected to the contact plate in a fluid-tight manner, forms a boundary of a fluid chamber having fluid flowing through it during operation of the fuel cell unit and is designed as a shaped sheet metal part.
Such a shaped sheet metal part may be produced from an essentially flat sheet metal blank by means of one or more shaping processes, in particular, by means of embossing and/or deep drawing. These production methods are considerably more suitable and more inexpensive for a large-scale production than the production of solid metal plates by way of milling or erosion.
In addition, it is possible to save on material and weight due to the use of shaped sheet metal parts.
The fluid flowing through the fluid chamber can be a combustible gas, an oxidation agent or a refrigerant.
In particular, it may be provided for the fluid chamber to be surrounded, apart from by the fluid guiding element, by the contact plate and by the cathode-anode-electrolyte unit.
In a preferred configuration of the invention it is provided for the cathode-anode-electrolyte unit of the fuel cell unit to be arranged on the fluid guiding element.
In particular, it may be provided for the cathode-anode-electrolyte unit to be arranged between the fluid guiding element, on the one hand, and the contact plate of the same fuel cell unit or an adjacent fuel cell unit, on the other hand.
The inventive fuel cell unit is already particularly simple to handle prior to the assembly of the composite block of fuel cells when the cathode-anode-electrolyte unit is held between the fluid guiding element and the contact plate of the same fuel cell unit.
Alternatively hereto, it may also be provided for the cathode-anode-electrolyte unit to be designed as a coating on the fluid guiding element or on the contact plate of the fuel cell unit.
It is particularly favorable when not only the fluid guiding element but also the contact plate is designed as a shaped sheet metal part. In this case, the contact plate of the fuel cell unit may also be produced in a simple manner by way of embossing and/or deep drawing from an essentially flat sheet metal blank which is more suitable and more inexpensive for a large-scale production than the production of solid contact plates by way of milling or erosion.
The contact plate and the fluid guiding element may, in this case, form a two-part shell of the fuel cell unit which surrounds the cathode-anode-electrolyte unit.
The inventive construction of a fuel cell unit is particularly suitable for so-called high-temperature fuel cell units which have an operating temperature of up to 950xc2x0 C. and can be operated, without any external reformer, directly with a hydrocarbonaceous combustible gas, such as, for example, methane or natural gas or alternatively hereto, using an external reformer, with a diesel or petroleum motor fuel.
For use in such a high-temperature fuel cell unit the shaped sheet metal parts, from which the fluid guiding element and also, where applicable, the contact plate of the fuel cell unit are formed, are produced from a sheet metal material which is chemically resistant at the resulting temperatures of up to 950xc2x0 C. in relation to the components of the combustible gas, the combustion air supplied and a refrigerant supplied where applicable (for example cooling air).
High-grade steel sheets resistant to high temperatures or steel sheets coated with an inorganic or ceramic material are particularly suitable for this purpose.
Furthermore, a sheet metal material is preferably selected which has a thermal coefficient of expansion compatible with that of the CAE unit.
The thickness of the sheet metal material used is preferably at the most approximately 3 mm, in particular, at the most approximately 1 mm.
In order to achieve a reliable connection between the contact plate and the fluid guiding element of the same fuel cell unit which is also resistant and gas-tight at high temperatures, it is preferably provided for the fluid guiding element and the contact plate to be connected to one another by way of welding, preferably by laser welding or by electron beam welding.
Alternatively or in addition hereto it may be provided for the fluid guiding element and the contact plate to be connected to one another by way of soldering, preferably by hard soldering.
In order to make the required compensation of charges between the CAE units of fuel cell units adjacent to one another possible in a simple manner it is provided in a preferred configuration of the inventive fuel cell unit for the fluid guiding element to have an opening for the passage of contact elements (e.g. of an adjacent fuel cell unit) to the cathode-anode-electrolyte unit.
In order to be able to hold the CAE unit between the fluid guiding element and the contact element of the fuel cell unit without shorting the anode and the cathode of the same fuel cell unit with one another, it is advantageously provided for the fluid guiding element to abut on the cathode-anode-electrolyte unit via an electrically insulating seal.
In a preferred configuration of the invention, the fluid guiding element is designed as a fluid guiding frame which abuts on the cathode-anode-electrolyte unit along the entire edge thereof via the electrically insulating seal.
It is particularly favorable when the seal between the fluid guiding element and the CAE unit comprises mica.
Alternatively or in addition hereto, it may be provided for the seal between the CAE unit and the fluid guiding element to comprise a flat seal.
Alternatively or in addition hereto, it may be provided for the seal between the CAE unit and the fluid guiding element to comprise a coating on the fluid guiding element and/or on the cathode-anode-electrolyte unit.
Such a coating may be applied, for example, by the screen printing method, by roller coating or by spray coating onto the fluid guiding element or the cathode-anode-electrolyte unit.
Inorganic or ceramic sealing media, which are chemically resistant, gas-tight and electrically insulating at an operating temperature of up to 950xc2x0 C., can be considered, in particular, for the sealing.
A solder glass can, for example, be used as sealing medium and this can be composed, for example, like a solder glass known from EP 0 907 215 A1, i.e. can contain 11 to 13% by weight of aluminum oxide (Al2O3), 10 to 14% by weight of boron oxide (BO2), approximately 5% by weight of calcium oxide (CaO), 23 to 26% by weight of barium oxide (BaO) and approximately 50% by weight of silicon oxide (SiO2).
Furthermore, it may be provided for the seal between the CAE unit and the fluid guiding element to be designed as a movable seal (slide fit sealing).
Furthermore, it may be provided for the fluid guiding element to be connected to the CAE unit by way of flanging.
It may, in particular, be provided for a flange fold area engaging around the CAE unit to be formed on the fluid guiding element.
In order to obtain the required pressing force for the sealing between the CAE unit and the fluid guiding element irrespective of any external biasing of the fuel cell units against one another, it is preferably provided for the cathode-anode-electrolyte unit and the fluid guiding element to already be biased elastically against one another on account of the geometry of the fuel cell unit and the connection between the fluid guiding element and the contact plate of the fuel cell unit.
In order to be able to use the fluid guiding element, apart from for holding the CAE unit, also for the formation of fluid channels, through which a fluid is supplied to the fuel cell unit or discharged from the same, it is provided in a preferred configuration of the invention for the fluid guiding element to be provided with at least one fluid port.
The area of the fluid guiding element surrounding the fluid port serves in this case as fluid guiding area of the fluid guiding element. A fluid channel then results from the fluid guiding areas of the fluid guiding elements of fuel cell units following one another in the stacking direction.
The fluid supplied or discharged via the fluid channel can be an oxidation agent or, preferably, a combustible gas.
It is particularly favorable when the holding means is provided with a fluid supply channel opening and with a fluid discharge channel opening. In this case, the fluid guiding element can be used not only for the formation of a fluid supply channel but also for the formation of a fluid discharge channel.
In order, during the formation of such fluid channels, to maintain the required electric insulation between the contact plates and fluid guiding elements of adjacent fuel cell units, it is advantageously provided for the fuel cell unit to comprise an electrically insulating fluid channel seal, via which the contact plate of the fuel cell unit abuts on the fluid guiding element of an adjacent fuel cell unit.
Alternatively or in addition hereto it may also be provided for the fuel cell unit to comprise a fluid channel seal, via which the fluid guiding element of the fuel cell unit abuts on the contact plate of an adjacent fuel cell unit.
Such a fluid channel seal may, for example, comprise a coating on the fluid guiding element and/or on the contact plate.
Such a coating may be applied, in particular, by the screen printing method, by roller coating or spray coating onto the fluid guiding element or the contact plate, respectively.
Inorganic and ceramic materials, which are chemically resistant, gas-tight and electrically insulating at the resulting operating temperatures of up to 950xc2x0 C., can be considered, in particular, as sealing media.
A particularly simple construction of the fluid channel seal results when this comprises a flat seal.
Particularly when the holding plate and the contact plate are connected to one another by flanging, it is of advantage when the fluid channel seal comprises at least two separate sealing elements which can be arranged, in particular, in different planes.
In order to compensate for different heat expansions, it is particularly favorable when the fluid channel seal comprises a slide fit sealing.
Particularly with a design as slide fit sealing it is of advantage when the fluid channel seal comprises a material, preferably a solder glass, viscous at the operating temperature of the fuel cell unit.
Claim 20 is directed to a composite block of fuel cells which comprises a plurality of inventive fuel cell units which follow one another along a stacking direction.
In order to be able to fix the individual fuel cell units of the composite block of fuel cells in their position relative to one another and, where required, to be able to generate an adequate contact pressure for the sealing between the CAE unit and the fluid guiding element and/or for the sealing between the fluid guiding element and the contact plate of an adjacent fuel cell unit, it is favorable when the composite block of fuel cells comprises at least one clamping element for bracing the fuel cell units against one another.
The composite block of fuel cells can, in particular, comprise two end plates which can be braced against one another by means of the clamping element.
In order to be able to supply a fluid (combustible gas, oxidation agent or refrigerant) to the composite block of fuel cells in a simple manner or discharge the fluid out of the composite block of fuel cells it is advantageously provided for at least one of the end plates to have at least one fluid port.
Bracing of the fuel cell units of the composite block of fuel cells against one another by means of a separate clamping element is superfluous when it is advantageously provided for the fluid guiding element of at least one of the fuel cell units to be connected to the contact plate of an adjacent fuel cell unit by way of flanging. This flanging is sufficient to secure the fuel cell units in their position relative to one another.
Nevertheless, an additional clamping element can be used in such a case to generate the contact pressure between the CAE units and the contact plates of the composite block of fuel cells.
It may, in particular, be provided for a flange fold area engaging around the contact plate of the adjacent fuel cell unit to be formed on the fluid guiding element of at least one of the fuel cell units.
Alternatively hereto, it may also be provided for a flange fold area engaging around the fluid guiding element of the adjacent fuel cell unit to be formed on the contact plate of at least one of the fuel cell units.
In a preferred configuration of the composite block of fuel cells it is provided for an electrically insulating fluid channel seal to be arranged between the flange fold area and the contact plate of the adjacent fuel cell unit. As a result of the flanging, such a fluid channel seal is already subject to the contact pressure required for an adequate sealing without any force of an external clamping system being required for this purpose.
In order to produce a composite block of fuel cells which comprises a plurality of inventive fuel cell units, a method is suitable which comprises the following method steps:
Assembly of the individual fuel cell units by arranging a cathode-anode-electrolyte unit between a contact plate and a fluid guiding element and gas-tight connection of the contact plate to the fluid guiding element;
subsequent assembly of the composite block of fuel cells by arranging a plurality of fuel cell units along a stacking direction and fixing the fuel cell units in their position relative to one another.
With such a method, the individual parts contact plate, CAE unit and fluid guiding element of a respective fuel cell unit are first of all fitted together and the contact plate and the fluid guiding element are connected to one another, for example, by welding or soldering in order to assemble the individual fuel cell unit.
Subsequently, the assembly of the entire composite block of fuel cells takes place, with which the fuel cell units of the composite block of fuel cells are preferably braced against one another by means of at least one clamping element.
In a special configuration of the method it may be provided for the fuel cell units of the composite block of fuel cells to be arranged between two end plates and for the two end plates to be braced against one another.
The method described above is suitable for the production of the composite block of fuel cells, in particular, when the fluid guiding element of at least one fuel cell unit abuts on the contact plate of an adjacent fuel cell unit via a flat seal or a slide fit sealing.
If, on the other hand, in the composite block of fuel cells to be produced the fluid guiding element of one fuel cell unit is connected to the contact plate of an adjacent fuel cell unit by way of flanging, a method which comprises the following method steps is particularly suitable for the production of such a composite block of fuel cells:
Assembly of several fluid guiding element-contact plate units by connecting a respective fluid guiding element of one fuel cell unit to a contact plate of an adjacent fuel cell unit by way of flanging;
formation of a stack consisting of fluid guiding element-contact plate units following one another along a stacking direction, wherein one respective cathode-anode-electrolyte unit is arranged between two such respective units;
gas-tight connection of the contact plates of the fuel cell units to the respective fluid guiding element of the same fuel cell unit.
With this method for the production of the composite block of fuel cells, the fluid guiding element of a first fuel cell unit is first of all preassembled with the contact plate of a second fuel cell unit by way of flanging, preferably at the combustible gas channel and at the discharge gas channel, wherein electrically insulating fluid channel seals are integrated into the respective flangings. Subsequently, the final assembly of the composite block of fuel cells is carried out in that the CAE units are arranged each time between the consecutive fluid guiding element-contact plate units and the contact plates and fluid guiding elements belonging to the same fuel cell unit, which hold a respective CAE unit between them, are connected to one another in a gas-tight manner by way of welding or soldering.